This disclosure relates to a method of controlling a hydraulic pumping system that is stationary while in operation with a fuel-driven drive with a motor for a pump, a heating device and an accumulator with a charge control system.
The disclosure relates in particular to a pumping system which is designed as a hydraulic pumping system, in particular with a plunger pump, for use in fracking, whereby the pumping system has no electrical network access, in particular no network access by an energy provider feeding its network with several power plants. Since the effects are regarded as advantageous for use in some exemplary embodiments for fracking, especially with a hydraulic pumping system, the disclosure is described below on the basis of this possible application.
A hydraulic pumping system for use in fracking includes, among other elements, a hydraulic pump, a motor and a transmission arranged on a trailer. There is also a tractor that can be coupled to the trailer. The engine of the tractor is coupled to the engine of the pump via a hydraulic system, via which the engine of the pump can be started. The starting process is effected by means of a hydraulic starter. A pre-lubrication pump builds up the oil pressure in the system during the starting process in order to reduce wear. The tractor engine can support the pumping system's electrical system, usually 24 V, when the pump engine is not running. The tractor is also used to transport the pumping system to different locations. An example of such a conventional system will be briefly explained later.
Several pumping systems are arranged at a drilling site, which are connected to each other via a manifold outside the trailers. During production, for example, a water-sand mixture is pumped into the ground at high pressure to break up rock strata, and the pumping systems typically remain at one drilling site for between 10 and 21 days, after which the pumping systems on the trailer are moved to the next drilling site by the tractor.
Hydraulic fracking takes place in several phases, also called stages, for example 20 to 30 phases. During one phase, for example, the water-sand mixture is pressed under high pressure into the ground. Between these phases, or stages, there is a resting phase, usually lasting one or more hours. During the resting phase the pumps do not deliver high pressure. According to the state of the art the pump motor remains in operation so that the pumping system is immediately ready for use again when the next phase is to be started.
In the context of the disclosure it was found that it is energetically inefficient to run the pump's motor during the rest periods. Although switching off the motor seems an obvious solution here, it was recognized in the context of the disclosure that this can lead to a significant cooling of the pump's motor, especially in cold ambient conditions. The resulting cold start of the motor leads to considerable wear and can lead to a loss of the manufacturer's warranty in the event of frequent cold starts.
Specifically, after 2 hours of production, there is typically a rest period of up to 4 hours. This means that pumping takes place for only about 35 hours on average per 100 hours of engine operation, while the engine runs inefficiently during the remaining time, i.e. during the rest periods. In addition, other power demanding electrical consumers have to be supplied on the trailer during the rest periods.
In the context of the disclosure it was also considered using a powerful electrical heater for the pump motor. However, it was recognized that such an electrical heater requires a very powerful—and therefore very expensive—accumulator due to the lack of mains access. Further, such an accumulator must be replaced regularly due to its limited service life, which leads to high operating costs.
In addition, the cost of the accumulator should be in proportion to the cost savings in motor maintenance costs. A larger or more powerful accumulator is generally not an economical solution. The disclosure makes it possible to keep the storage capacity of the accumulator as small as possible while at the same time achieving cost savings in the operating costs of the motor.